fix(security): land the 2026-07 audit fixes — SSRF guards, roster lane, SYSTEM path hygiene

The low/medium findings from the July host+Windows security review, as
implemented in the audit session's working tree:

- Webhooks and library-art fetches refuse loopback/link-local/metadata
  targets and no longer follow redirects (SSRF pivots from the privileged
  host process).
- The paired-client rosters (/clients, /native/clients) move off the
  streaming-client auth lane — one paired device could enumerate every other
  device's name + fingerprint; only the bearer/loopback console keeps them.
- Device-name sanitizing extends to bidi/format control characters
  (spoofable rendering) via the shared native_pairing::is_spoofy_char;
  stream-marker quoting uses the same set.
- The SYSTEM service resolves powershell by its full System32 path —
  CreateProcess checks the launching EXE's own directory first, so a planted
  powershell.exe beside the host binary would have run as SYSTEM.
- The pf-vdisplay driver's opt-in file log moves from world-writable
  C:\Users\Public to WUDFHost's own temp dir.
- GameStream pairing sessions are single-use (removed whatever the outcome).
- Uninstall also removes the pf_mouse driver-store entry (rider from the
  virtual-HID-mouse work).
- openapi.json regenerated (hardened-config-dir doc wording).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/punktfunk-host/src/library/lutris.rs

@@ -102,6 +102,19 @@ fn lutris_art(slug: &str) -> Artwork {
 #[cfg(target_os = "linux")]
 fn lutris_image(kind: &str, slug: &str) -> Option<String> {
     use base64::Engine as _;
+    // `slug` comes verbatim from Lutris's `pga.db` (untrusted at this layer). Reject any path
+    // separator, parent ref, or NUL so a crafted slug can't escape the art roots and read an
+    // arbitrary `<slug>.jpg` off disk — the bytes are base64-inlined into the `/api/v1/library`
+    // JSON a paired client can GET, so an escape is an arbitrary-file-read exfil primitive
+    // (security-review 2026-07-17). Real Lutris slugs are `[a-z0-9-]`.
+    if slug.is_empty()
+        || slug.contains('/')
+        || slug.contains('\\')
+        || slug.contains("..")
+        || slug.contains('\0')
+    {
+        return None;
+    }
     let home = std::env::var_os("HOME").map(PathBuf::from)?;
     let roots = [
         home.join(".local/share/lutris"),